Stabilized vinyl aromatic compounds



Patented July 24, 1 951 It:

2,561,915 I STABILIZED VINYL AROMATIC COMPOUNDS Edwin R. Erickson, Molin'e, IllL," assignor to V Mathieson Chemical Corp'oratioma corporation of Virginia 1 i N Drawing. Application March '11, 1947,

Serial No. 733,989 H 4 Claims. (01. 260 -650) (jew l)! STATES PATENT" oFF cE l l 2 My invention relates to a method of inhibiting for its polymerization inhibitin action. In genthe polymerization of polymerizable vinyl comeral, I prefer those hydrocarbon chlorides conpounds, particularly polymerizable vinyl comtaining an intermediate number of carbon atoms, pounds, such as nuclear dichlorostyrene, which viz., from about 4 to 12 carbon atoms, and I parare hi hly active in the respect of polymeriza- 5 ticularly prefer those containing a number of tion. The invention embraces as compositions of carbon atoms within the lower portion of this matter, polymerizable vinyl aromatic compounds range. Thus, tertiary butyl chloride is a parto which have been added the inhibitors employed ticularly preferred hydrocarbon chloride for use in the practice of the method. in the practice of my invention.

The inhibitors herein referredto include those Substituted hydrocarbon groups which may disclosed in my copending application Serial No. form part of the molecule of the polyhydroxy 528,777 filed March 30, 1944, now Patent No. compound with which the hydrocarbon chloride 2,455,746 dated December 7, 1948. is reacted may also comprise oxygen, as an ether Polymerizable vinyl aromatic compounds find inkage, for example, or they may contain one or wide'application in industry in the manufacture I 5 more halogen atoms or hydroxy radicals, for. exof plastics and synthetic rubbers. Their use for ample. Similarly to the case of the hydrocarbon such purposes follows from their ability to polychloride it is preferred that groups attached to merize either additively or'with each other, or the ring nucleus of the 'polyhydroxy compound with other polymerizable monomers, aliphatic contain at least 4 but not more than about 12 dien'es;such as butadiene, for example. For ob- ,20 carbon atoms, but groupscontaining a greater vious reasons premature polymerization of a vinyl or'lesser number of carbon atoms are not witharomatic compound, occurring as during shipout the scope of the invention. ment or storage or during a distillation operation f The reaction in the presence of stannic chloride being conducted for the purpose of purifyin the is believed to yield, essentially, a condensate commonomeric material, i undesirable. a

In accordance with the present invention, I redrocarbon halide. As a matter of convenience, tard or prevent the polymerization of polymerthe reaction product will be hereinafter referred izable vinyl aromatic compounds by incorporating to as a substituted polyhydro'xy benzene."

therewith the product obtained when a hydro- My invention is based onthe discovery that a carbon chloride is reacted, in the presence of substitutedpolyhydroxy'benzene prepared by a s'tannic chloride, with a compound of the for-- condensation reaction involving the use of stannic mula'; chloride as the condensing agent is far more effective as an inhibitor of the polymerization of OH vinyl aromatic compounds than substituted poly- R1 hydroxy-benzenes prepared with other condensing I agents, zinc chloride, ferric chloride, or aluminum chloride,'forexample. -I cannot ofier any R3 explanation for-thi phenomenom- Many organo in which R1, R2, and R3 may be hydrogen, hytin compounds which I tested proved to be very droxy, .or a substituted or unsubstituted hydro- 40 1 1I1h1b1trS-- a carbon group, and in which R4 and R5 may be hys pr vi us tim d; e u st tuted polydrogen or a substituted or unsubstituted hydro- Yd f Y be zen'es prepared With'stannic chloride carbon group; provided, however, that at least as the Condensing agent'are P cula y efiective one unsubstituted hydrogen atom is present and polymerization inhibitors ffir-substitution p -f that at least one of R1 and R3 is hydroxy. Preucts of styrene, such as nuclear dichlorostyrene, ferred compounds Within the scope of the formula which p y r s more r a y than Styrene are-hydmquinbne, ateehol and pyrOsa self. Howeverpmy inhibitors can be used with Hydrocarbon chlorides employed in the pracstyrene with excellent results, also with styrene tice of the invention include alkyl, aryl, alkaryl, m less a dsu u du ts w e t vand alicyclic chlorides containing from 1 toupitywith'respect- 1J p me i n ompares With wards of 18 carbon atoms. Elements other than s y e I g j halogen, oxygen, for example, or radicals such Among the many compounds otherthan nuclear ashydroxy, may be present in the molecule where dichlorostyrene to which my invention may be thereis no interference with the reaction or with applied'may be mentioned: nuclear alkylated stythe properties of' the reaction product responsible renes, alpha-alkyl styre essuch as alpha-methyl and alpha-ethyl styrene, alpha-alkyl styrene halostyrenes, nuclear chlorostyrenes containing more than 2 nuclear chlorine atoms, the styrene compound derived from ethyl p-ethyl-benzoate proportion of inhibitor: varies the particular vinyl aromatic treatment to which the compound is to be subjected prior to its ultization. In some cases, an amount as low as about 0.001% on the weight of the vinyl aromatic compound may be adequate. Generally, less than 1% of; the inhibitor is sufiicient, but larger amounts up to about 5% or more may be used, especially if the vinyl are; matic compound is apt to be exposed to conditions favoring its premature polymerization. Where the substituted polyhydroxy benzene is insufficiently soluble in the polymerizable monomer, a mutual solvent for the inhibitor and the monomer may be used.

Incorporation of the inhibitor in the vinyl aromatic compound may be accomplished simply by addition of the inhibitor with stirring, but in large scale operations it may be more advantageous to effect the incorporation in some other way as by percolating the vinyl aromatic compound through a layer or bed of the inhibitor. Many of the inhibitors, because of their substantial solubility, may be conveniently incorporated by preparing a concentrated solution of the inhibitor-in the monomer to be stabilized and adding this concentrated solution to larger quantities of the monomer.

The substituted polyhydroxy benzenes may be used individually or in admixture or they may be used in conjunction with other inhibitors. Where protection against polymerization is desired in a distillation operation, it is frequently advantageous to employ two inhibitors, one of which is substantially less volatile than the monomer being distilled, and the other of which is slightly more volatile. In this way the pro tection extends throughout the distillation system since the higher boiling inhibitor will prevent polymerization in the kettle, while the lower boiling inhibitor will prevent polymerization in the fractionating column. In a few cases, it is possible to select an inhibitor whose volatility characteristics are such that while it will remain largely in thekettle a sufficient quantity will distill at the operating temperature to afford adequate protection in the column.

My inhibitors are readily removed by simply washing the stabilized material with an aqueous solution of an alkali, such as caustic soda, or the like.

My invention is illustrated by the following specific examples which are in part comparative. In the induction test referred to in the examples, a given amount of the inhibitor is :added to nuclear dichlorostyrene and the inhibited mixture heated over a boiling water bath. Samples of the mixture are removed periodically and added to a small amount of methanol. Since polymeric dichlorostyrene is insoluble irimethanol easily observable white curds form when polymerization has started in the mixture being heated. The number of minutes heating before the curds form is a measure of the effectiveness of the inhibitor and is designated the induction period. The induction period on uninhibited dichlorostyrene is from 1 to 3 minutes.

Example 1 340 gms. of tertiary butyl chloride was refiuxed with 88 gms. of catechol and 17.9 gms. of stannic chloride for about 30 minutes. On cooling, the mixture solidified. The solid was washed on a filter with cold ligroin, air dried, and pulverized. 0.1% of the material in nuclear dichlorostyrene gave an induction period of 217 minutes.

For comparison, the experiment was repeated using zinc chloride as the condensing agent. In this case the induction period was only 30 minutes. With aluminum chloride the result was evenpoorer, the induction period being only 14 minutes.

For still further comparison, 5 gms. of-ferric chloride, 44 gms. of catechol and 200 ml. of tertiary butyl chloride were similarly refluxed, and the product washed, dried and tested. 0.5% of the product in dichlorostyrene gave an induction period of only 21 minutes.

Example 2 A mixture of 25.2 gms. of pyrogallol, 150 ml. of tertiary butyl chloride and 4 ml. of stannic chloride was refluxed for minutes. The cooled mixture was diluted with 75 ml. of ligroin and placed in a refrigerator for two hours. Thereafter part of the solvent was distilled off under reduced pressure and the residue cooled to crystallize out the product which was filtered and washed with cold ligroin. 0.1% of the product in dichlorcstyrene gave induction periods of 62 and 67 minutes in two tests. Prepared using other metal chlorides as the condensing agent the product gave an induction period of only 38 minutes when dissolved to the extent of 0.25% in dichlorostyrene.

Example 3 Monotertiary butyl catechol was reacted with tertiary butyl chloride in the presence of a minor amount of stannic chloride. 0.05% of the product in dichlorostyrene gave an induction period of 133 minutes as compared with 21 minutes when the product was prepared using condensing agents other than stannic chloride.

Example 4 A mixture of 37 grams of 2,5 dihydroxydiphenyl, '75 ml. of tertiary butyl chloride and 1 ml. of stannic chloride was refluxed for 45 min.- utes. At the end of the reaction '75 ml. of ligroin was added and the mixture cooled to crystallize out the product which when dissolved in dichlorostyrene to the extent of 0.05% gave an induction period of 92 minutes.

Example 5 A mixture containing 33.2 gms. of tertiary butyl catechol, 42 gms. of mixed chloroethyldichlorobenzenes having a refractive index of 1.55213.- 1.5590 and 1 ml. of stannic chloride was refluxed in 50 ml. of hexane for 3.5 hours. Upon comple-. tion of the reaction 156 ml. of hexane was added and the hot solution filtered through charcoal. .After removal of excess solvent by distillation under reduced pressure, a black solid was obtained which when dissolved in dichlorostyrenes to the in which R1, R2 and R3 are radicals selected Irom the group consisting of hydrogen, hydroxy and a hydrocarbon group, and in which R4 and R5 are radicals selected from the group consisting of hydrogen and a hydrocarbon group; provided, however, that at least one hydrogen atom is preschi; and that at least one of R1 and R3 is hydroxy.

2. Nuclear dichlorostyrene which has been stabilized against polymerization by the incorporation of a small amount of the product obtained by reacting tertiary butyl chloride and hydroquinone at reflux temperature in the presence of stannic chloride.

3. Nuclear dichlorostyrene which has been stabilized against polymerization by the incorporation of a small amount of the product obtained by reacting tertiary butyl chloride and catechol at reflux temperature in the presence of stannic chloride. I

4. Nuclear dichlorostyrene which has been stabilized against polymerization by the incorporation of a small amount of the product obtained by reacting tertiary butyl chloride and pyrogallol at reflux temperature in the presence of stannic chloride.

EDWIN R. ERICKSON.

REFERENCES CITED The following references are. of record in the file of this patent:

' UNITED STATES PATENTS Number Name Date 2,181,102 Stoesser et al Nov. 21, 1939 2,212,478 Miller Aug. 20, 1940 2,295,077 Dreisbach et a1. Sept. 8, 1942 

1. A NORMALLY POLYMERIZABLE VINYL AROMATIC COMPOUND WHICH HAS BEEN STABILIZED TO PREVENT ITS POLYMERIZATION BY THE INCORPORATION OF A SMALL AMOUNT OF THE PRODUCT OBTAINED BY REACTING AT REFLUX TEMPERATURE AND IN THE PRESENCE OF A CATALYTIC AMOUNT OF STANNIC CHLORIDE, A HYDROCARBON CHLORIDE AND A COMPOUND OF THE FORMULA, 